CN107343024A - A kind of centralized car networking MAC layer merges prediction of collision and avoiding method - Google Patents
A kind of centralized car networking MAC layer merges prediction of collision and avoiding method Download PDFInfo
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Abstract
The invention discloses a kind of centralized car networking MAC layer to merge prediction of collision and avoiding method, belongs to vehicular ad hoc network field.This method allows double bounce scope exterior node timeslot multiplex, improves time interval resource utilization ratio.Free timeslot collection is can access in RSU time slots broadcast node first per slot cycle RSU, new node is according to the random selection time slot access of this time slot collection；Then RSU by via node obtain in the range of vehicle position, speed and time slot occupancy situation, prediction merge collision occur possibility；Last RSU adjustment time slot distributes and broadcasts adjustment result, effectively avoids merging collision.This method is assisted by timeslot multiplex and RSU, reduces the probability of happening for merging collision, so as to reduce MAC layer Message Time Delay, increases handling capacity.The mac-layer protocol that the present invention can send broadcast message as vehicular ad hoc network interior joint uses.
Description
Technical field
The present invention relates to multichannel media access control MAC (Media in the car networking in wireless communication technology field
Access Control) agreement, and in particular to a kind of centralized car networking MAC layer merges prediction of collision and avoiding method.
Background technology
Intelligent transportation system (Intelligent Transportation Systems, ITS) is a kind of with real-time, high
Effect, the novel traffic transportation system of accuracy.The demand of safe driving, car networking VANET are existed with ITS development and people
The communication coordinated between car and car, car and road side facility is widely studied.
Car networking channel resource is limited, how to be efficiently the most important thing of research using existing channel.Need to pass in car networking
Defeated message is divided into security message and media information, and traditional IEEE1609.4 is a kind of multiple channels access side based on time segmentation
Formula, it divides time into the 100ms cycles, and preceding 50ms is control channel time slot, and node is in control channel time slot broadcast safe information
And control frame；50ms is service channel time slot afterwards, and node transmits media information in service channel time slot, and vehicle node antenna is being controlled
Channel services channel processed alternately switches.This mode can guarantee that the low time delay of security message, but channel utilization is relatively low, and handling capacity is not
It is high.
With going deep into for research, because vehicle node information transfer is limited in scope, timeslot multiplex, which turns into, improves channel utilization
Major way.VeMAC proposes the timeslot multiplex mode of vehicle node, and which allows the outer time slot of node double bounce scope to answer
With.Vehicle node uses distribution topology mode, and Time Slot Occupancy collection in the range of itself double bounce of each node maintenance, media information exists
Two nodes successfully match the transmission of rear steering service channel.This mode improves channel throughput, but due to car speed not
Disconnected change, merging collision probability of happening is larger, causes security message to obtain in time, time delay increases therewith.RSU(Rode
Side unit, roadside unit) existing for Centralized Topology can in a big way it is interior pool vehicle node utilization of resources situation,
Channel resource utilization ratio rationally can be improved using RSU synergism, optimizes network performance.
The content of the invention
The present invention is low for existing car networking MAC protocol channel utilization, the high phenomenon of time delay, it is proposed that one kind is based on section
The centralized car networking MAC layer of point relative velocity merges prediction of collision and avoiding method, by there is RSU centralization topology knot
Structure, RSU predictions are collided and coordinate time slot service condition, to ensure relatively low merging collision rate, reduce network delay.
The purpose of the present invention can be reached by adopting the following technical scheme that：
A kind of centralized car networking MAC layer merges prediction of collision and avoiding method, methods described comprise the following steps：
S1, roadside unit RSU are that the new vehicle node into RSU regions broadcasts accessible idle optional time slot in all directions
Collect E (x), wherein, RSU regions are divided into four parts, every portion according to the double bounce scope that geographical position and vehicle node message are transmitted
Divide a corresponding specific via node time slot；
S2, newly enter RSU regions vehicle node according to idle optional time slot collection E (x) random selection time slot access；
S3, newly sentence into RSU regions vehicle node according to Time Slot Occupancy set N (x) in the range of neighbor node time slot double bounce
It is disconnected itself whether to be successfully accessed, access collision also whether occurs；If judgement accesses collision, newly enter RSU regions vehicle section
Point repeat step S2, step S3；
S4, RSU are that vehicle selects via node vehicle in RSU regions, and are the corresponding relaying of via node vehicle distribution
Node slot time, renewal time slot distribution list T (x)；
S5, via node vehicle via node time slot information aggregate from vehicle to RSU unicast self zones；
S6, RSU are according to vehicle location, speed in the range of the RSU of via node transmission and take slot prediction merging collision
A situation arises；
S7, RSU prediction, which merge collision, to be occurred, then change relative velocity in two vehicle nodes for taking identical time slot
Time slot shared by larger node, and change result is added into time slot distribution list T (x)；If do not have to merge collision, directly
Into step S8；
In RSU time slot time slot distribution list T (x), each node monitors list and updates itself shared time slot by S8, RSU.
Further, RSU carries out trunk node selection, via node according to trunk node selection algorithm in the step S4
With closest to regional center position PEi, closest to current vehicle flowrate average speedPossessing highest signal strength ERSSI (d) is
Most preferably, wherein, the trunk node selection algorithm is specially：
Wi=w1*Distance+w2*Velocity-w3*NRSSI(di)
Wherein Distance is normalized cumulant of the vehicle node to each central area positions of RSU, and its calculation formula is as follows：
Velocity is that the normalizated velocity of vehicle node and current vehicle flowrate averag density is poor, and its calculation formula is as follows：
NRSSI(di) be vehicle node i normalized signal intensity, its calculation formula is as follows：
PiFor the position coordinates of node i, specially Pi=(xi,yi), PEiFor node i region center position coordinates, it is
Fixed value, specially PEi=(xa,ya), ViFor the instantaneous velocity of node i,It is averaged for vehicle node in vehicle i travel directions
Speed, RSSI (d) they are Link State judgment models, whereinWiFor node i
Weight results, RSU select W in four partsiMinimum node is the via node of each several part.
Further, the Link State judgment models are specially using the multipath fading model for having shadow effect：
RSSI (d)=PTi-L-10nlog(d)+f(μ,σ)
Wherein PTiFor node transmitting power, L is constant power attenuation, and n washes one's face and rinses one's mouth for path loss, d be node i to RSU it
Between distance, f (μ, σ) is shadow fading model, obey it is expected μ=0, Gaussian Profile of the standard deviation sigma between 6-12dB.
Further, each cycle of the time slot is divided into three parts, and Part I is vehicle node time slot, wherein pressing
It is divided into two subdivisions according to vehicle heading, respectively left orientation running vehicle node time slot and during dextrad driving vehicle node
Gap, Part II are via node time slot, and Part III is RSU time slots.
Further, it is random according to idle optional time slot collection E (x) that RSU regions vehicle node is newly entered in the step S2
Select time slot access mode for：
Random selection some free timeslot consistent with displacement direction, and broadcast the traveling side of itself in this time slot
To, position and velocity information.
Further, RSU regions vehicle node is newly entered in the step S3 according in the range of neighbor node time slot double bounce
Time Slot Occupancy set N (x) judges that the mode whether itself is successfully accessed is：
The node slot time that each node collects neighbor node broadcast in the range of itself jump takes set Nj(x) and update certainly
The Time Slot Occupancy set N of bodyi(x), newly added node is by monitoring the node slot time that neighbor node is broadcasted in next slot cycle
Set is taken, judges itself to whether there is in this set and is consistent with itself selected time slot, judge whether successfully to obtain with this
To time slot or access collision occurs.
Further, the content of the information aggregate of vehicle in the self zone that via node vehicle is broadcasted in the step S5
Including：Node ID, travel direction, speed, position, transmission power, shared time slot ID.
Further, the process of the step S6 is specific as follows：
Step S61, RSU extractions take speed, the positional information of identical time slot node；
Step S62, RSU calculates the relative position of two vehicle nodes in next slot cycle, and prediction merges collision
Situation, if in next slot cycle, two node relative positions are less than two hop distances of vehicle node transmission range, then judge
Merging collision may occur；If in next slot cycle, two node relative positions are more than the two of vehicle node transmission range
Hop distance, then judge that merging collision can not possibly occur.
Further, the process of the step S7 is specific as follows：
Step S71, after RSU predictions merging collision may occur, the node larger according to nodal information access speed, and be
Selected node chooses time slot again；
Step S72, RSU is that selected node chooses time slot again according to stochastic selection algorithm, chooses time slot and judges institute afterwards
Time slot ID is selected to whether there is in vehicle node time slot collection, if carrying out next step judgement in the presence of if, if being not present, for this node weight
It is new to choose time slot；Whether time slot selected by judging in next step is free timeslot, and it is this node slot time that RSU is then represented if free timeslot
Choose successfully, if not free timeslot, then judge to get the section of new time slot according to the merging collision predicting method in step S6
Point whether can occur with other nodes it is new merge collision, if judging, merging collision may occur, and be chosen again for this node
Time slot, if judging, not having new merging collision occurs, then it represents that RSU is that this node slot time chooses success again；
Step S73, this time slot is reselected result and adds time slot distribution list T (x) by RSU.
Further, it is assumed that vehicle travels on two-way traffic bidirectional high speed highway, and RSU maintenance spans radius is 400m, can be managed
The vehicle condition in its front and rear 800 meters of link length is managed, it is 100m that node one, which jumps transmission range, and vehicle is obeyed into RSU regions
Poisson distribution, vehicle travel along track in certain speed range internal speed-changing.
The present invention is had the following advantages relative to prior art and effect：
1) Centralized Topology is used, RSU Central Regulation time slot service conditions, present node can be met to greatest extent
Density situation, improve channel service efficiency；
2) a situation arises according to the association attributes of its scope interior nodes judgement merging collision by RSU, adjusts Time Slot Occupancy collection
Close, reduce and merge collision probability of happening.
Brief description of the drawings
Fig. 1 is vehicle topology diagram in the present invention
Fig. 2 is structure of time slot figure in the present invention
Fig. 3 is the flow chart that centralized car networking MAC layer disclosed by the invention merges prediction of collision and avoiding method；
Fig. 4 is the flow chart that new node adds network in the present invention；
Fig. 5 is RSU predictions collision and the flow chart avoided in the present invention；
Fig. 6 is the flow chart of RSU changes collision node slot time in the present invention.
Embodiment
To make the purpose, technical scheme and advantage of the embodiment of the present invention clearer, below in conjunction with the embodiment of the present invention
In accompanying drawing, the technical scheme in the embodiment of the present invention is clearly and completely described, it is clear that described embodiment is
Part of the embodiment of the present invention, rather than whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art
The every other embodiment obtained under the premise of creative work is not made, belongs to the scope of protection of the invention.
Embodiment
In the present embodiment, road model constraint is as follows：Vehicle travels on two-way traffic bidirectional high speed highway.RSU(Rode
Side unit, roadside unit) maintenance span radius is 400m, the vehicle condition in its front and rear 800 meters of link length can be managed.
It is 100m that node one, which jumps transmission range,.
As shown in figure 1, vehicle, which enters RSU regions, obeys Poisson distribution, vehicle is along track in certain speed range internal speed-changing
Traveling.RSU region divisions are as shown in figure 1, RSU regions are divided into according to the double bounce scope that geographical position and vehicle node message are transmitted
Four parts, a corresponding specific via node time slot per part.RSU obtains the information of vehicle node in RSU regions, including
Speed, position, transmission power etc..
This method time dividing mode is：As shown in Fig. 2 each slot cycle is divided into three parts, Part I is
Vehicle node time slot, wherein be divided into two subdivisions according to vehicle heading, respectively left orientation running vehicle node time slot and
Dextrad driving vehicle node slot time, Part II are via node time slot, and Part III is RSU time slots.When node possesses itself
In itself shared time slot broadcast N (x) after gap.
As shown in Figure 3,4, centralized car networking MAC layer disclosed in the present embodiment merges prediction of collision and avoiding method and included
Following steps：
Step S1, roadside unit RSU is accessible idle optional in the new vehicle node broadcast all directions into RSU regions
Time slot collection E (x).
Roadside unit RSU is the optional time slot collection E of newly added node broadcast idle according to current time slots node occupancy situation
(x), E (x) refers to the free timeslot in the range of newly added node double bounce, and its content is in the range of newly added node opening position double bounce
Free timeslot collection, it is allowed to double bounce scope exterior node timeslot multiplex.RSU ensures that newly added node will not be with having taken the section of time slot
Point occurs to merge collision；
Vehicle node listens to first slot cycle and terminated after entering RSU regions, it is assumed that its node ID is 08, is obtained
The E (x) of RSU broadcast, as shown in table 1.
The idle optional time slot sets E (x) of table 1.
Step S2, RSU regions vehicle node is newly entered according to idle optional time slot collection E (x) random selection time slot access.
Random selection time slot access way is that newly added node is listened to after idle optional time slot collection E (x), random choosing
Some free timeslot consistent with displacement direction is selected, and itself travel direction, position and speed are broadcasted in this time slot
Etc. information.
The new free timeslot consistent with itself travel direction and access into 08 node random selection E (x), access side
Formula is to broadcast nodal information in the range of itself jump in selected time slot, and adds itself selected node and itself speed, position etc.
Information.Assuming that 08 node travel direction is L, its selected time slot ID is 07.
Step S3, RSU regions vehicle node is newly entered according to Time Slot Occupancy set N in the range of neighbor node time slot double bounce
(x) judge whether itself is successfully accessed, access collision also whether occurs；If judgement accesses collision, newly enter RSU regions car
Node repeat step S2, step S3.
Newly into RSU regions vehicle node judge that the method for itself access slot success or not is, each node collected from
The node slot time of neighbor node broadcast takes set N in the range of the jump of body onej(x) and the Time Slot Occupancy set N of itself is updatedi(x),
Newly added node takes set by monitoring the node slot time that neighbor node is broadcasted in next slot cycle, judges whether itself deposits
It is consistent in this set and with itself selected time slot, judges whether successfully to get time slot with this or access collision occurs.
Nodal information set N (x) in the range of the double bounce of table 2.
Newly added node 08 monitors time slot in the range of the node double bounce that next cycle neighbor node is safeguarded and accounts for set N (x), such as
Shown in table 2.Judge whether itself is successfully accessed by the occupancy situation of time slot in N (x), if N (x) displays of neighbor node newly connect
Ingress ID is consistent with its selected time slot, then it represents that is successfully accessed.Above step is repeated if failure and reselects time slot.Table 2
Show the success of 08 access slot of vehicle node 07.
Step S4, RSU is that vehicle selects via node vehicle in RSU regions, and corresponding for the distribution of via node vehicle
Via node time slot, renewal time slot distribution list T (x).
RSU carries out trunk node selection according to trunk node selection algorithm, and via node is with closest to regional center position
PEi, closest to current vehicle flowrate average speedIt is optimal to possess highest signal strength ERSSI (d).Method is：
Wi=w1*Distance+w2*Velocity-w3*NRSSI(di)
Wherein Distance is normalized cumulant of the vehicle node to each central area positions of RSU, and its calculation formula is as follows：
Velocity is that the normalizated velocity of vehicle node and current vehicle flowrate averag density is poor, and its calculation formula is as follows：
NRSSI(di) be vehicle node i normalized signal intensity, its calculation formula is as follows：
PiFor the position coordinates of node i, specially Pi=(xi,yi), PEiFor node i region center position coordinates, it is
Fixed value, specially PEi=(xa,ya)。ViFor the instantaneous velocity of node i,For in vehicle i travel directions vehicle node it is flat
Equal speed.RSSI (d) is Link State judgment models, whereinWiFor node i
Weight results, RSU select four parts in WiMinimum node is the via node of each several part.
Above-mentioned Link State judgment models use the multipath fading model for having shadow effect, are specially：
RSSI (d)=PTi-L-10n log(d)+f(μ,σ)
Wherein PTiFor node transmitting power, L is constant power attenuation, and n washes one's face and rinses one's mouth for path loss, d be node i to RSU it
Between distance, f (μ, σ) is shadow fading model, obey it is expected μ=0, Gaussian Profile of the standard deviation sigma between 6-12dB.
After node successfully obtains time slot, RSU selection closest to current vehicle flowrate average speed, positioned at regional center position,
The node for possessing good link state is via node, and distributes via node time slot for via node.System of selection as above,
RSU selects WiMinimum node is via node.RSU is that via node distribution via node time slot is as shown in table 3.Assuming that region
W in one06Minimum, then node 06 be chosen as the via node in region one, node 06 in addition to the particular time-slot 03 for possessing itself,
RSU distributes a via node time slot 93 for it, as shown in table 3, the time slot corresponding node 06 of 03 time slot corresponding node 06,93, table
It is the via node in region one to show 06, wherein assuming that the corresponding via node time slot in region one is 93.
Time Slot Occupancy set T (x) before table 3.RSU adjustment
Step S5, information aggregate of the via node vehicle in via node time slot vehicle into RSU unicast self zones；
The content of the information aggregate of vehicle is in the self zone of via node vehicle broadcast：Node ID, travel direction, speed
Degree, position, transmission power, shared time slot ID.Per the 100ms cycles, via node collects itself maintenance area interior nodes information, and
Broadcasted in via node time slot, broadcasted content set is as shown in table 4.
Itself institute maintenance span interior nodes information aggregate N of the relay node broadcasts of table 4.06(x)
Step S6, RSU is pre- according to the information such as vehicle location, speed and occupancy time slot in the range of the RSU of via node transmission
Surveying merging collision, a situation arises.
Step S61, RSU extractions take the information such as the speed of identical time slot node, position；
Step S62, RSU calculates the relative position of two vehicle nodes in next slot cycle, if in next time slot week
In phase, two node relative positions are less than two hop distances of vehicle node transmission range, then judge that merging collision may occur；If
In next slot cycle, two node relative positions are more than two hop distances of vehicle node transmission range, then judge to merge collision
It can not possibly occur；
RSU calculates the relative position for taking identical time slot node in next slot cycle, and prediction merges collision, and a situation arises.
Forecasting Methodology is：(Vi-Vj)×T≥D-2R.Wherein ViAnd VjThe respectively instantaneous velocity of node i and j, T grow for slot cycle
Degree, D are the distance between node i and node j, and R is that node one jumps transmission range, is dimensioned to 100m.
Step S7, RSU predictions merge collision and may occurred, then change relative in two vehicle nodes for taking identical time slot
Time slot shared by the larger node of speed, and change result is added into time slot distribution list T (x)；If not having to merge collision,
It is directly entered step S8；
Step S7 detailed processes are as follows：
Step S71, after RSU predictions merging collision may occur, the node larger according to nodal information access speed, and be
Selected node chooses time slot again；
Step S72, RSU is that selected node chooses time slot again according to stochastic selection algorithm, chooses time slot and judges institute afterwards
Time slot ID is selected to whether there is in vehicle node time slot collection, if carrying out next step judgement in the presence of if, if being not present, for this node weight
It is new to choose time slot；Whether time slot selected by judging in next step is free timeslot, and it is this node slot time that RSU is then represented if free timeslot
Choose successfully, if not free timeslot, then judge to get the section of new time slot according to the merging collision predicting method in step S6
Point whether can occur with other nodes it is new merge collision, if judging, merging collision may occur, and be chosen again for this node
Time slot, if judging, not having new merging collision occurs, then it represents that RSU is that this node slot time chooses success again；
Step S73, this time slot is reselected result and adds time slot distribution list T (x) by RSU.
Flow is as shown in Figure 6.In the method, it is that the stochastic selection algorithm that node reselects time slot is：I'=(i+
P) %m.Wherein i is conflict time slot ID, p=12, -12,22, -22..., k2,-k2,M grows for vehicle node time slot collection
Degree.
Assuming that node 01 and node 32 use same time slot 01, RSU is predicted in next He of 100ms periodic knots 01
The distance between node 03 is less than two hop distances, and merging collision may occur, then updates time slot distribution list T (x).Assuming that node
32 relative velocities are larger, then RSU changes T (x) interior joint 32 possesses time slot, is changed to it from 01 according to random selection method
02, judge that time slot 02 is present but not for free timeslot, node 05 takes time slot 02.Whether RSU decision nodes 32 can occur with 05
Merge conflict, it is assumed that node 32 may occur to merge to conflict with section 05, then return and reselect time slot；Time slot is reselected again
For 01, it may occur however that merge collision, return reselects time slot；It is 05 to reselect time slot again, judges 05 for free timeslot,
Then time slot is chosen successfully, and node 32 takes time slot 05, and RSU updates time slot distribution list T (x), as shown in table 5.
Time Slot Occupancy set T (x) in the embodiment of table 5. after RSU adjustment
Step S8, RSU in RSU time slot time slot distribution list T (x), monitor list and update shared by itself by each node
Time slot.
Above-described embodiment is the preferable embodiment of the present invention, but embodiments of the present invention are not by above-described embodiment
Limitation, other any Spirit Essences without departing from the present invention with made under principle change, modification, replacement, combine, simplification,
Equivalent substitute mode is should be, is included within protection scope of the present invention.
Claims (10)
1. a kind of centralized car networking MAC layer merges prediction of collision and avoiding method, it is characterised in that methods described includes following
Step：
S1, roadside unit RSU are that the new vehicle node into RSU regions broadcasts accessible idle optional time slot collection E in all directions
(x), wherein, RSU regions are divided into four parts according to the double bounce scope that geographical position and vehicle node message are transmitted, right per part
Answer a specific via node time slot；
S2, newly enter RSU regions vehicle node according to idle optional time slot collection E (x) random selection time slot access；
S3, newly judge certainly according to Time Slot Occupancy set N (x) in the range of neighbor node time slot double bounce into RSU regions vehicle node
Whether body is successfully accessed, and access collision also whether occurs；If judgement accesses collision, newly enter RSU regions vehicle node weight
Multiple step S2, step S3；
S4, RSU are that vehicle selects via node vehicle in RSU regions, and distribute corresponding via node for via node vehicle
Time slot, renewal time slot distribution list T (x)；
S5, via node vehicle via node time slot information aggregate from vehicle to RSU unicast self zones；
S6, RSU are according to vehicle location, speed and the hair for taking slot prediction merging collision in the range of the RSU of via node transmission
Raw situation；
S7, RSU prediction, which merge collision, to be occurred, then it is larger to change relative velocity in two vehicle nodes for taking identical time slot
Node shared by time slot, and will change result add time slot distribution list T (x)；If not having to merge collision, it is directly entered
Step S8；
In RSU time slot time slot distribution list T (x), each node monitors list and updates itself shared time slot by S8, RSU.
2. a kind of centralized car networking MAC layer according to claim 1 merges prediction of collision and avoiding method, its feature exist
In RSU carries out trunk node selection according to trunk node selection algorithm in the step S4, and via node is with closest in region
Heart position PEi, closest to current vehicle flowrate average speedIt is optimal to possess highest signal strength ERSSI (d), wherein, it is described
Trunk node selection algorithm is specially：
Wi=w1*Distance+w2*Velocity-w3*NRSSI(di)
Wherein Distance is normalized cumulant of the vehicle node to each central area positions of RSU, and its calculation formula is as follows：
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<mrow>
<mi>m</mi>
<mi>i</mi>
<mi>n</mi>
</mrow>
</msub>
</mrow>
</mfrac>
</mrow>
Velocity is that the normalizated velocity of vehicle node and current vehicle flowrate averag density is poor, and its calculation formula is as follows：
<mrow>
<mi>V</mi>
<mi>e</mi>
<mi>l</mi>
<mi>o</mi>
<mi>c</mi>
<mi>i</mi>
<mi>t</mi>
<mi>y</mi>
<mo>=</mo>
<mfrac>
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<msub>
<mi>V</mi>
<mi>i</mi>
</msub>
<mo>-</mo>
<mover>
<mi>V</mi>
<mo>&OverBar;</mo>
</mover>
<mo>|</mo>
</mrow>
<mrow>
<mo>|</mo>
<mi>V</mi>
<mo>-</mo>
<mover>
<mi>V</mi>
<mo>&OverBar;</mo>
</mover>
<msub>
<mo>|</mo>
<mi>max</mi>
</msub>
<mo>-</mo>
<mo>|</mo>
<mi>V</mi>
<mo>-</mo>
<mover>
<mi>V</mi>
<mo>&OverBar;</mo>
</mover>
<msub>
<mo>|</mo>
<mi>min</mi>
</msub>
</mrow>
</mfrac>
</mrow>
NRSSI(di) be vehicle node i normalized signal intensity, its calculation formula is as follows：
<mrow>
<mi>N</mi>
<mi>R</mi>
<mi>S</mi>
<mi>S</mi>
<mi>I</mi>
<mrow>
<mo>(</mo>
<msub>
<mi>d</mi>
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<mi>S</mi>
<mi>I</mi>
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<msub>
<mi>d</mi>
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<mi>I</mi>
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<mi>d</mi>
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<mi>R</mi>
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<mi>d</mi>
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</mrow>
<mrow>
<mi>m</mi>
<mi>i</mi>
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</msub>
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</mrow>
PiFor the position coordinates of node i, specially Pi=(xi,yi), PEiFor node i region center position coordinates, for fixation
Value, specially PEi=(xa,ya), ViFor the instantaneous velocity of node i,For the average speed of vehicle node in vehicle i travel directions
Degree, RSSI (d) is Link State judgment models, whereinWiFor the power of node i
It is worth result, RSU selects W in four partsiMinimum node is the via node of each several part.
3. a kind of centralized car networking MAC layer according to claim 2 merges prediction of collision and avoiding method, its feature exist
In,
The Link State judgment models use the multipath fading model for having shadow effect, are specially：
RSSI (d)=PTi-L-10n log(d)+f(μ,σ)
Wherein PTiFor node transmitting power, L is constant power attenuation, and n washes one's face and rinses one's mouth for path loss, and d is node i between RSU
Distance, f (μ, σ) are shadow fading model, obey and it is expected μ=0, Gaussian Profile of the standard deviation sigma between 6-12dB.
4. a kind of centralized car networking MAC layer according to claim 1 merges prediction of collision and avoiding method, its feature exist
In each cycle of the time slot is divided into three parts, and Part I is vehicle node time slot, wherein according to vehicle heading
It is divided into two subdivisions, respectively left orientation running vehicle node time slot and dextrad driving vehicle node slot time, during Part II is
After node slot time, Part III is RSU time slots.
5. a kind of centralized car networking MAC layer according to claim 1 merges prediction of collision and avoiding method, its feature exist
In newly into RSU regions vehicle node according to idle optional time slot collection E (x) random selection time slot access in the step S2
Mode is：
Random selection some free timeslot consistent with displacement direction, and this time slot broadcast itself travel direction,
Position and velocity information.
6. a kind of centralized car networking MAC layer according to claim 1 merges prediction of collision and avoiding method, its feature exist
In newly into RSU regions vehicle node according to Time Slot Occupancy set N in the range of neighbor node time slot double bounce in the step S3
(x) judge that the mode whether itself is successfully accessed is：
The node slot time that each node collects neighbor node broadcast in the range of itself jump takes set Nj(x) and itself is updated
Time Slot Occupancy set Ni(x), newly added node is taken by monitoring the node slot time that neighbor node is broadcasted in next slot cycle
Set, judge itself to whether there is in this set and be consistent with itself selected time slot, when judging whether successfully to get with this
Gap or generation access collision.
7. a kind of centralized car networking MAC layer according to claim 1 merges prediction of collision and avoiding method, its feature exist
In the content of the information aggregate of vehicle includes in the self zone that via node vehicle is broadcasted in the step S5：Node ID, OK
Sail direction, speed, position, transmission power, shared time slot ID.
8. a kind of centralized car networking MAC layer according to claim 1 merges prediction of collision and avoiding method, its feature exist
In the process of the step S6 is specific as follows：
Step S61, RSU extractions take speed, the positional information of identical time slot node；
Step S62, RSU calculates the relative position of two vehicle nodes in next slot cycle, and prediction merges collision, and a situation arises,
If in next slot cycle, two node relative positions are less than two hop distances of vehicle node transmission range, then judge to merge
Collision may occur；If in next slot cycle, two node relative positions be more than vehicle node transmission range double bounce away from
From then judgement merges collision and can not possibly occurred.
9. a kind of centralized car networking MAC layer according to claim 1 merges prediction of collision and avoiding method, its feature exist
In the process of the step S7 is specific as follows：
Step S71, after RSU predictions merging collision may occur, the node larger according to nodal information access speed, and be selected
Node chooses time slot again；
Step S72, RSU is that selected node chooses time slot again according to stochastic selection algorithm, when choosing selected by time slot judgement afterwards
Gap ID whether there is in vehicle node time slot collection, if carrying out next step judgement in the presence of if, if being not present, be selected again for this node
Take time slot；Whether time slot selected by judging in next step is free timeslot, then represents that RSU chooses for this node slot time if free timeslot
Success, if not free timeslot, then the node for judging to get new time slot according to the merging collision predicting method in step S6 is
It is no can occur with other nodes it is new merge collision, if judging, merging collision may occur, and time slot is chosen again for this node,
If judging, not having new merging collision occurs, then it represents that RSU is that this node slot time chooses success again；
Step S73, this time slot is reselected result and adds time slot distribution list T (x) by RSU.
10. a kind of centralized car networking MAC layer according to any one of claims 1 to 9 merges prediction of collision and avoiding method,
It is characterized in that, it is assumed that vehicle travels on two-way traffic bidirectional high speed highway, and RSU maintenance spans radius is 400m, before can managing it
Vehicle condition in 800 meters of link lengths afterwards, it is 100m that node one, which jumps transmission range, and vehicle enters RSU regions and obeys Poisson point
Cloth, vehicle travel along track in certain speed range internal speed-changing.
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